This invention relates to new process technology for the production of epoxides from olefins. More particularly this invention relates to the epoxidation of olefins using a new catalytic system.
It is known in the art that olefins can be oxidized to their respective epoxides with hydrogen peroxide in the presence of a peroxotungstate catalyst; see e.g., U.S. Pat. No. 5,274,140 to Venturello et al. (two-phase system), and U.S. Pat. No. 5,780,655 to Shum (single-phase system). It is also known that tungsten compounds are poor catalysts for epoxidation of isolated olefins with aqueous H2O2 in monophasic systems unless water is continuously removed. See in this connection, Venturello et al., J. Org. Chem. 1983, 48, 3831, which cites Payne et al., J. Org. Chem. 1959, 24, 54, Hori et al., id., 1978 43, 1689, and Pralus et al., Fundamental Research in Homogeneous Catalysis, M. Tsutsui, ed., Plenum, New York, 1979, Vol. 3, pp. 327-343 and references therein.
Other activities on catalytic epoxidation of olefinic compounds include, for example, work reported in U.S. Pat. Nos. 4,303,586, 4,303,587, 4,562,276, and 4,595,671, and in Venturello et al., J. Org. Chem., 1988, 53, 1553 and Venturello et al., Synthesis Communications, 1983, 295.
Heretofore azeotropic distillation has been utilized in connection with a single-phase reaction mass in order to continuously remove water so as to maintain a single organic phase in the reaction mass. In particular, a catalyst system was prepared by adding Na2WO4.2H2O, H2SO4, and a quaternary ammonium halide to 1-hexene, and heating this mixture while stripping off water from the mixture. Then, concentrated aqueous hydrogen peroxide was added to the resultant mixture, whereby a peroxotungstate catalyst was formed in situ, which catalyzed exothermic epoxidation of 1-hexene to 1,2-epoxyhexane. During the reaction, water and organics were continuously azeotropically stripped from the reactor, so that a single organic liquid phase was maintained in the reactor. The organic portion of the distillate was separated from the water, and recycled to the reactor. The reaction was discontinued when the epoxide concentration in the reactor reached a desired level in the range of 40-50 weight percent. While satisfactory results were achieved this way, it would be desirable to have a longer-lived catalyst that maintains the high selectivity of the reaction.
This invention provides tungsten-catalyzed epoxidation processes having a longer-lived catalyst that maintains the high selectivity of the reaction.
It has been found that the inclusion of boric acid and an alkanediol in a tungsten-based catalyzed epoxidation reaction, preferably a peroxotungstate-catalyzed epoxidation reaction, prolongs the life of the catalyst while improving the selectivity of the catalyst and suppressing peroxide decomposition.
In one of its embodiments this invention provides a process of forming an epoxide, which process comprises epoxidizing in the liquid phase, an olefinic compound (preferably an olefinic hydrocarbon), with hydrogen peroxide in the presence of a catalytic quantity of a tungsten-based catalyst system (preferably a peroxotungstate catalyst system), wherein (i) boric acid and (ii) at least one alkanediol individually and/or as a reaction product of (i) and (ii) are being or have been included in the liquid phase.
Another embodiment is a process of forming an epoxide, which process comprises:
A) continuously feeding aqueous hydrogen peroxide solution into a reaction mixture formed from components comprising at least one olefinic hydrocarbon to which have been added (i) tungstic acid and/or a tungsten compound, preferably a tungsten (VI) compound, and an inorganic acid, (ii) an onium compound, preferably a quaternary ammonium compound, (iii) boric acid and (iv) at least one alkanediol and/or (v) a borate ester-containing mixture formed from boric acid and at least one alkanediol, such that at least one epoxide is formed; and
B) continuously or substantially continuously removing water from the reaction mixture by distillation so that at least during substantially the entire time the aqueous hydrogen peroxide is being fed, the reaction mixture has a liquid phase which is a single liquid phase or an essentially single liquid phase.
A preferred embodiment is a process of forming an epoxide, which process comprises:
A) continuously cofeeding (1) aqueous hydrogen peroxide solution and (2) at least one olefinic hydrocarbon, into a reaction mixture formed from components comprising (a) at least one olefinic hydrocarbon (b) a tungsten compound, preferably (i) tungstic acid and/or (ii) a tungsten (VI) compound and an inorganic acid, (c) an onium compound, preferably a quaternary ammonium compound, and (d) boric acid and (e) at least one alkanediol and/or (f) a borate ester-containing mixture formed from boric acid and at least one alkanediol, such that at least one epoxide is continuously being formed; and
B) continuously or substantially continuously removing water from the reaction mixture by distillation so that at least during substantially the entire time the aqueous hydrogen peroxide is being fed, the reaction mixture has a liquid phase which is a single liquid phase or an essentially single liquid phase.
These and other embodiments and features of the invention will become still further apparent from the ensuing description and appended claims.